1. Field of the Invention
The present invention relates to a roof lining for a vehicle roof, to a method for producing the same and to the use thereof in a vehicle roof.
2. Description of the Related Art
Vehicle roof linings are important components for the interior lining of vehicles. Essentially, they affect the acoustic characteristics of the vehicle, they should be aesthetically pleasing and should be sufficiently stiff in order to support accessories such as, for example, sun visors, interior lighting, ventilation slits, clothes hooks etc. Furthermore these linings should be lightweight, should be economically manufacturable, should be easy to install, and should fulfil a number of criteria (fire resistance, emission of toxic or noxious fumes etc.).
Vehicle parts having large surface areas, in particular vehicle roofs, tend to vibrate on traveling on account of their low inherent stability. This behavior is conventionally counteracted by mounting damping material, in particular heavy layers containing bitumen. Traditionally multi-layered roof lining elements are used which have only an aesthetic function and serve to support accessories.
An acoustically effective roof lining is known, for example, from EP 0,255,332, and comprises a semi-flexible carrier layer with which, in the manner of a snap closure, the roof lining can be tensioned against the vehicle roof. With this carrier layer a classic spring-mass-system with a resilient, sound-absorbing foam layer and a visco-elastic, closed-pored heavy layer (filled with bitumen) is pressed against the vehicle roof.
EP 0,637,820 for example discloses a sound absorbing roof lining, which essentially comprises an approximately 5–15 mm thick, semi-rigid polyurethane (PU) foam layer and a 4–10 mm thick, spring elastic compound fiber layer, both layers being permeable to air. In this embodiment, the foam layer is reinforced on both its sides with glass fibers and, on the passenger compartment side, comprises an air permeable décor layer. The individual layers are, in turn, connected to each other by means of an air permeable adhesive layer, and in particular by a PU-adhesive. However, this sound absorbent roof lining is a classical spring-mass-system or a classical foam absorber.
As it is the general aim of the automobile industry to reduce the weight of vehicles, these systems have proven to be too heavy for modern requirements of the automobile industry. As a result, ever thinner and lighter lining elements are used, which however, have an insufficient acoustic effectiveness, for example for sound absorption purposes, and in particular in the range below 1000 Hz.
Multi-layered vehicle roof linings are also known which are lightweight and stiff, but which also have a poor acoustic performance.
Thus, FR 2,503,721 suggests a lightweight roof lining, which essentially comprises a porous and glass fiber reinforced foam layer being covered with a décor layer, and having an air-impermeable polyethylene foil between the décor layer and the glass fiber reinforced foam layer in order to prevent the permeation/penetration of adhesive components through the décor layer. This foil results in an insufficient acoustic absorption capacity of the roof lining, which could possibly be improved by applying perforations. However, such perforations in the polyethylene foil can cause visually perceptible changes to the décor layer.
Therefore, in WO98/18657 there is described an ultra-light, multifunctional assembly, with which an excellent acoustic comfort in the vehicle interior can be achieved, and at the same time achieving a weight reduction of about 50% in comparison to linings having a classic spring-mass-system and an improved aesthetic durability. This publication describes the composition of an acoustically and aesthetically satisfactory vehicle roof lining, however without describing the method of manufacture.